1. Technical Field
The present invention relates to a motor-operated valve destined to control the flow rate of fluids, for example, a refrigerant used in air conditioners.
2. Description of the Conventional Art
The structure of a motor-operated valve invented by the Applicant of the present invention is disclosed in detail in the Japanese Published Unexamined Application No. 101765 of 2008. As disclosed in this patent document, the motor-operated valve uses a mechanical paradox planetary gear mechanism to considerably reduce the speed of rotation of a stepping motor provided to let the valve disc ascend and descend, thereby providing micro-flow control of a refrigerant or the like.
FIG. 4 shows the structure of a motor-operated valve similar to that disclosed in the Japanese Published Unexamined Application No. 101765 of 2008. In FIG. 4, the essential parts of the motor-operated valve are shown hatched.
This motor-operated valve is designed to be larger in bore diameter of the valve element than disclosed in the cited patent document and accordingly the front end of the valve element is enlarged correspondingly to the increase in bore diameter of the valve seat.
As shown, the motor-operated valve includes a body 10 having formed therein a valve chamber 14 and an orifice 16 communicating with the chamber 14.
The body 10 has connected thereto a pipe 12a at the side of the orifice 16 and a pipe 12b at the side of an opening formed in the side wall of the chamber 14. Also the body 10 has inserted and fixed in the upper portion of the chamber 14 thereof a bush 20.
The bush 20 has an internal thread 22 formed on the inner wall of the central bore thereof. A base plate 28 is firmly fixed to the top of the body 10. A bottomed cylindrical can 30 is installed on the base plate 28.
On the outer circumference of the can 30 there is fitted a stator member generally indicated with a reference sign 40. The stator member 40 includes a yoke 44 and a coil 46 wound on a bobbin provided inside the yoke 44. These elements of the stator member 40 are wholly covered with a plastic member 42. The coil 46 is supplied with a power through a lead wire 48. The stator member 40 and a rotor member 50 pivotally supported inside the can 30 form together a stepping motor.
The rotor member 50 made of a magnetic material is connected integrally with a sun gear member 51 made of a plastic material, and a shaft 62 is inserted in the central portion of the sun gear member 51. The shaft 62 is inserted and supported at the upper portion thereof in a hole formed in a support member 60 provided inside the upper portion of the can 30, and at the lower portion thereof in a hole formed in the upper portion of a shank 70a which will be further described later.
The sun gear member 51 includes a sun gear 52 which is in mesh with a plurality of planetary gears 55 supported pivotably on a plurality of shafts 54, respectively, provided upright on a carrier 53. Each of the planetary gears 55 is axially long and in mesh at the upper half thereof with a ring gear 58 mounted on the top of a cylindrical member 24 installed on the top of the bush 20.
The planetary gear 55 is in mesh at the lower half thereof with an internal gear 71 of an annular output gear 70.
The above-mentioned gears form together a so-called “mechanical paradox planetary gear mechanism”. With the ring gear 58 and the internal gear 71 of the output gear 70 being designed a little different in number of teeth from each other, it is possible to reduce the rotation of the sun gear 52 at a large ratio for transmission to the output gear 70.
The output gear 70 has a downward extending shank 70a firmly fixed to the center of the lower surface thereof. A slit 73a is formed in the lower portion of the shank 70a. Also a driver 72 is provided. The driver 72 has formed at the top thereof a flat convexity (flat plate-shaped portion) 73b which is to be inserted in the slit 73a in the shank 70a. The slit 73a and flat plate-shaped portion 73b form together a coupling which connects the output gear 70 and driver 72.
The driver 72 has an external thread 74 formed thereon. The external thread 74 is in mesh with the internal thread 22 formed inside the bush 20. Thus, the driver 72 moves axially while rotating. This axial movement of the driver 72 is transmitted to a shaft-shaped valve element 80 through a ball-shaped pressing member 76. The ball-shaped pressing member 76 prevents the rotation of the driver 72 from being transmitted to the valve element 80.
The body 10 has fixed therein a tubular spring case 90 having a small-diameter portion 90c. Guided by the lower small-diameter portion 90c of the tubular spring case 90, the valve element 80 is moved axially. In this motor-operated valve cited herein by way of example, a flange 90a is provided at the top of the spring case 90. It is held between the upper end face of a small-diameter portion formed at the top of the body 10 and the lower surface of the bush 20, and thus the spring case 90 is fixed inside the body 10.
A spring shoe member 84 is firmly fixed at the top of the valve element 80, and a coil spring 92 is provided compressed between the lower surface of a large-diameter portion 84d formed at the top of the spring shoe member 84 and a stepped portion 90b of the spring case 90. The coil spring 92 normally forces the valve element 80 in a direction in which the valve is opened.